In an electrostatic accelerator, an electrostatic generator is used to accumulate electrical charge on a high voltage electrode which is insulated from the ground. One particularly effective high voltage generator utilizes a series of conductive charge carrying pellets fixed along a chain with insulating elements extending between the pellets. Such a system is disclosed in U.S. Pat. Nos. 3,469,118 and 3,612,919, of which I am co-inventor. In a typical electrostatic accelerator, the high voltage electrode is contained in a pressure vessel which contains high pressure gas, typically sulfur hexafluoride, which resists electrostatic breakdown between the high voltage electrode and the vessel which is grounded. An insulative column supports the high voltage electrode and extends between the grounded vessel and the high voltage electrode. One or more high voltage acceleration tubes extend between the high voltage electrode and the ground. The tubes are comprised of alternating insulative elements with conducting elements.
An even voltage gradient is maintained between the high voltage electrodes and the ground by allowing a small mount of current from the high voltage electrode to cascade down the conductive elements of the acceleration tube through high value resistors which connect the conductive elements. To further improve the shape of the electrostatic field, conductive hoops are placed around the acceleration tube or tubes and again, a small, generally lesser value of current is allowed to cascade down the outer hoops. Thus, a smooth gradient between the high voltage electrode and the ground is produced. Particles, such as electrons, protons, and other positively or negatively charged ions, may be accelerated by injecting them into the acceleration tube so they pass between the high voltage electrode and the ground.
Electrostatic generators are capable of producing extremely high voltages ranging up to over 25 million volts. Such high voltage generators have been widely used in the construction of potential drop accelerators. Historically, ion accelerators have been used in particle physics and condensed matter physics to probe the fundamental laws of nature.
Over time industrial uses have arisen for particle accelerators. For example, the acceleration of doping ions in the semi-conductor field has allowed the precise injection of ions into substrates to form transistors and other semiconductor devices. In the tool industry, the capability of selectively implanting ions into the surface of materials has been used to develop new surface-hardening techniques.
Recently a demand for a high current source of protons or deuterons has been supplied by high current non-electrostatic accelerators. Electrostatic accelerators have not been capable of supplying the high currents necessary for supplying the proton or deuteron beam necessary for certain applications involving the production of gamma rays by proton or deuteron bombardment.
It has been known for many years that, in the construction of a free electron laser using a Van de Graff type electron accelerator, electrons can be recycled to improve the efficiency of the devices.
What is needed is an apparatus and method for facilitating the use of electrostatic accelerators in applications requiring high proton or deuteron beam currents.